The subject application is directed generally to color printing, and is particularly directed to improving color rendering of printed documents in accordance with ink or output medium characteristics of a particular output device. The application teaches a system and method wherein a sculpted gamut having improved output characteristics on a color rendering device is isolated and selected as a gamut disposed between those full gamuts associated with CMY and CMYK device colorants or toners.
As an introduction, a color space is typically a particular model of colors. For color image rendering devices, such as color printers, including ink jet printers, laser printers, solid color printers or dye sublimation printers, images are typically created by selective placement of color from a subtractive primary color system. Subtractive color primary systems function by selectively removing one or more colors from a multi-color light source, such as white light. This is to be contrasted with an additive primary color system wherein colors are created by selective addition of light of various wavelengths to achieve a desired color output. An additive color spectrum, such as red-green-blue (RGB) is suitably used in an active device, such a color display or color projector.
Common subtractive primary colors include the primary color set of cyan-magenta-yellow (CMY). Selectively mixing various proportions of these three colors allows for creation of various colors. An amount of each of these primary colors can be varied from 0% to 100%. Pure cyan is suitably denoted as (100, 0, 0), pure magenta as (0, 100, 0) and pure yellow as (0, 0, 100). Since three degrees of freedom can define a three dimensional object in a three-dimensional space, it will be appreciated that varying each component between 0% to 100% relative to one another will generate a three dimensional, six surface cube in color space which encompasses all possible colors that can be rendered with the primary set. This CMY cube is referred to as a gamut in this device color space.
Addition of black to the CMY color space results in a color space referred to as CMYK. With the addition of black, the resultant color gamut is extended beyond that of CMY in the shadows. The CMYK device color space is suitably modeled as a dodecahedron, which is a twelve surface solid. The addition of K is suitably modeled by separating the top and bottom 3 surfaces of the CMY cube and maintaining connecting along edges and corners. This forms the dodecahedron whose greater volume is reflective of the greater gamut extent of the CMYK device color space.
Use of CMYK permits better visual rendering of color images by increasing the tonal range. However, care must be taken in its application in order to avoid introduction of visual artifacts in an output image.